Mechanical leech in a case, c 1850.

Image number: 10284557

The practice of bleeding, or bloodletting, was intended to drain 'poisons' or excess blood from the body in order to restore the balance of the humours. Bleeding was a popular therapy in the Middle Ages, and continued to be practised as late as the 19th century. In 1833, France imported over 40 million medicinal leeches.